The production of polypeptides with target protein-binding properties is of great economic interest. At present, a number of methods have been developed to screen large libraries and identify polypeptides with binding affinity to a protein of interest. Typically, a large number of genetically diverse polypeptide mutants are produced in a first step. In a second step these polypeptide mutants are selected according to their binding affinity to the protein of interest. This process for the production of diversity and subsequent targeted selection can be repeated as often as it is desired.
However, a protein that has high target binding affinity may not have sufficiently high stability and solubility. Even for those proteins that have high solubility, high concentration liquid formulations tend to have short shelf lives and may lose biological activity as a result of chemical and physical instabilities during the storage. For example, aggregate formation during storage of a liquid protein composition can adversely affect the biological activity of the protein, resulting in loss of therapeutic efficacy and/or an increase in immunogenicity in humans.
This application provides an improved screening method for the selection of target-binding proteins having desirable biophysical properties (e.g., high solubility, stability, etc.). The method combines mRNA display and yeast surface display in a way that takes advantage of the desirable attributes of both processes.